allout-layout is a variable defined in `allout.el'.
Its value is

  • Automatically becomes buffer-local when set.
  • This variable is safe as a file local variable if its value
    satisfies the predicate which is a byte-compiled expression.

Buffer-specific setting for allout layout.

In buffers where this is non-nil (and if `allout-auto-activation'
has been customized to enable this behavior), `allout-mode' will be
automatically activated. The layout dictated by the value will be used to
set the initial exposure when `allout-mode' is activated.

*You should not setq-default this variable non-nil unless you want every
visited file to be treated as an allout file.*

The value would typically be set by a file local variable. For
example, the following lines at the bottom of an Emacs Lisp file:

;;;Local variables:
;;;allout-layout: (0 : -1 -1 0)

dictate activation of `allout-mode' mode when the file is visited
(presuming proper `allout-auto-activation' customization),
followed by the equivalent of `(allout-expose-topic 0 : -1 -1 0)'.
(This is the layout used for the allout.el source file.)

`allout-default-layout' describes the specification format.
`allout-layout' can additionally have the value `t', in which
case the value of `allout-default-layout' is used.